The herpesviruses comprise a large family of double stranded DNA viruses. The herpesvirus family can be divided into three subfamilies (.alpha., .beta., .gamma.) based upon a number of biological properties such as host range and tropism, viral life cycle, and viral persistence and latency. Eight of the herpesviruses, herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), and human herpes viruses 6, 7, and 8 (HHV-6, HHV-7, and HHV-8), have been shown to infect humans.
HSV-1 and HSV-2 are the prototypic .alpha.-herpesviruses. These two serotypes share approximately 50% nucleotide homology. Both are neurotropic viruses, but their primary sites of replication are different. HSV-1 typically infects the oral mucosa resulting in ulcerations commonly referred to as cold sores. HSV-2 infects and causes ulcerations of the genital mucosa. HSV infection can also result in disseminated disease and encephalitis, especially in immunocompromised patients. D. O. White and F. J. Fenner, In Medical Virology, D. O. White and F. J. Fenner, eds., Academic Press, p. 318-347 (1994).
VZV is also an .alpha.-herpesvirus and is the causitive agent of chicken pox. VZV establishes a latent infection in the dorsal root ganglia of the peripheral nervous system. From its latent site, VZV can cause recurrent disease commonly referred to as shingles or zoster. The probability of shingles increases with age and frequently occurs in immunocompromised patients. A. M. Arvin, In Virology, B. N. Field, D. M. Knipe, and P. M. Howley, ed., Lippincott-Raven Press, New York, p. 2547-2586 (1996).
Human cytomegalovirus (HCMV), a .beta.-herpesvirus, is an ubiquitous agent producing infection in individuals of all age groups. Infection rates of 60-100%, depending on geographic area and socioeconomic status have been reported. R. J. Whitley, S. Goldsmith and J. Gnann, In Society for General Microbiology. 45th Symposium: Control of Virus Diseases, Mimmock, N.J.; P. D. Griffiths and C. R. Madely, eds., Cambridge University Press, Cambridge, p. 315 (1990). The majority of infections are asymptomatic. However infections occuring in the immunocompromised patient, including organ transplant recipients and individuals with AIDS may be severe and include HCMV induced pneumonia, colitis, and retinitis. L. W. Drew, Clin. Infect. Dis. 14:608-615 (1992). HCMV is the leading cause of blindness in AIDS patients. T. C. Merigan and S. Resta, Rev. Infect. Dis.12: S693 (1990). HCMV also establishes lifelong latency in the host.
HCMV DNA polymerase (HCMV pol) is an enzyme essential for viral replication. D. H. Spector, K. M. Klucher, D. K. Rabert and D. A. Wright, In Herpesvirus Transcription and Its Regulation, E. K. Wagner, ed., CRC Press, Boca Raton, Fla., p. 261 (1991). The current therapies for HCMV; Ganciclovir, Foscarnet and Vistide act by inhibition of HCMV pol. A. K. Field and K. K. Biron, Clin. Micro. Reviews 7:(1) 1-13 (1994). See also U.S. Pat. Nos. 4,199,574; 4,215,113; 4,355,032; and E. DeClercq et al., Antiviral Research, Vol 8, pages 261-272 (1987). Ganciclovir and Foscarnet display significant toxicity and induction therapy is restricted to an intravenous route of administration. D. Faulds and R. C. Heel, Drugs, 39:597 (1990). Maintenance therapy with Ganciclovir and Foscarnet will likely contribute to drug resistant virus. A. K. Field and K. K. Biron, Clin. Micro. Reviews 7:(1) 1-13 (1994). Clearly less toxic, orally bioavailable alternatives are needed.
EBV is a .gamma.-herpesvirus which replicates in the epithelial cells of the nasopharynx and salivary glands and resides latently in B-cells. Childhood infections of EBV are normally asymptomatic. However, EBV infection is associated with several diseases in adults such as infectious mononucleosis, Burkitt's lymphoma, nasopharyngeal carcinoma, and Hodgkins disease. A. B. Rickinson and E. Kieff, In Virology, B. N. Fields, D. M. Knipe, and P. M. Howley, eds., Lippincott-Raven Press, New York, p. 2397-2446 (1996).
HHV-6 is a .beta.-herpesvirus which causes roseola (exanthem subitum) in children. P. Lusso, Antivir. Res. 31:1-21 (1996). HHV-7 shares 50-60% nucleotide sequence homology with HHV-6. It's disease association is unclear, but it may be involved in some cases of roseola. N. Frenkel and E. Roffman, In Virology, B. N. Fields, D. M. Knipe, P. M. Howley, eds., Lippincott-Raven Press, New York, p. 2609-2622 (1996). HHV-8, also known as Kaposi's sarcoma associated herpesvirus (KSHV), is a .gamma.-herpesvirus which has recently been associated with Kaposi's sarcoma in AIDS patients and multiple myeloma. M. B. Rettig et al., Science, 276:1851-1854 (1997).